The photonic network that supports current backbone networks is mainly formed by optical communication apparatuses such as wavelength multiplexing transmission apparatuses, optical add-drop apparatuses and optical cross-connect apparatuses, transmission routes such as optical fibers connecting these optical communication apparatuses, and paths such as wavelengths connecting between optical communication apparatuses via the transmission routes. Especially, research and development of the transparent type photonic network techniques is getting a lot of attention for connecting between optical communication apparatuses from end to end in the photonic network using a path without regenerative relay processing of optical signals in the relay sections.
In the following, a conventional optical communication apparatus of the transparent type photonic network is described.
The optical communication apparatus is mainly formed by an interface including transmission function and receiving function of a main signal, a wavelength multiplexing-demultiplexing unit, a route exchange unit such as an optical switch, and a control unit (refer to non-patent document 1, for example).
An optical communication apparatus in the entrance side of the path converts a main signal received from a client into an optical signal at the interface and outputs it, and the route exchange unit properly switches the destination of the output optical signal. In addition, the wavelength multiplexing-demultiplexing unit multiplexes optical signals to be transmitted to the same adjacent optical communication apparatus, and outputs the multiplexed signal to the same transmission route. In an optical communication apparatus of the exit side of the path, the wavelength multiplexing-demultiplexing unit demultiplexes the optical signals input via the transmission route into each wavelength, and the route exchange unit switches each of the demultiplexed optical signals into a proper destination interface. In addition, the interface converts the optical signal into the main signal, and transmits the main signal to a communication apparatus in the client side. In the optical communication apparatus at the relay side, the wavelength multiplexing-demultiplexing unit demultiplexes the optical signals input via the transmission route into each wavelength, and switches the route of the optical signal for each wavelength. Further, the wavelength multiplexing-demultiplexing unit multiplexes the optical signals to be transmitted to the same adjacent optical communication apparatus, and outputs the multiplexed signal to the same transmission route.
It is expected that the above-mentioned optical communication technique realizes economy of the photonic network since the technique reduces electrical processing in the interfaces of the optical communication apparatuses in the relay section so that the number of interfaces in the photonic network is reduced.
Also, research and development of path control techniques is active for dynamically changing connections between optical communication apparatuses by flexibly controlling paths. For example, a technique is realized for increasing/decreasing the number of paths connecting between two optical communication apparatuses according to traffic amount flowing in the paths (refer to non-patent document 2, patent document 1, patent document 2, patent document 3, for example).
According to the above-mentioned optical communication technique, it becomes possible that paths connecting between optical communication apparatuses share limited wavelength resources (frequency resources) in optical fibers according to bandwidth demand based on the traffic amount, so that it is expected that the wavelength resources (frequency resources) of the photonic network can be further economized.
However, the past interface cannot demultiplex and decode, for each wavelength, multiplexed main signals or optical signals in which frequency bands are overlapping. In addition, the past wavelength multiplexing-demultiplexing unit cannot demultiplex, for each wavelength, the multiplexed main signals or optical signals in which frequency bands are overlapping. Therefore, it is necessary to design and manage main signals or optical signals input and output in one transmission route such that frequency bands do not overlap. Also, past interfaces perform frequency control beforehand on main signals or optical signals to be output to the same transmission route such that frequency bands do not overlap, and output the signals to the same transmission route.
On the other hand, due to development of optical transmission techniques after 2005, it becomes possible to demultiplex and decode, for each wavelength, the main signals or optical signals in which frequency bans are overlapping (refer to non-patent document 3, for example), so that effective use of the limited wavelength resources (frequency resources) in the optical fiber is beginning to be expected.